All basic AC systems use a refrigeration cycle such as shown in FIG. 1. The refrigeration cycle is performed by a coolant flow through a condenser coil, an expansion valve, an evaporator coil and a compressor.
In the refrigeration cycle, a heat pump transfers heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction due to the second law of thermodynamics. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile the compressor is driven by a belt connected to a pulley on the engine's crankshaft, with both using electric motors for air circulation. Since evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively pump a refrigerant through the system. A refrigerant is pumped into the low pressure compartment (the evaporator coil), where, despite the low temperature, the low pressure causes the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapor is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space. The heat exchanger in the condenser section (the heat sink mentioned above) is cooled most often by a fan blowing outside air through it, but in some cases can be cooled by other means such as water, especially on some ships, geothermal and cooling towers.
Air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishments, large open chiller cabinets act as highly effective air dehumidifying units.
Some air conditioning units dry the air without cooling it. They work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about ⅓ of the electricity. They are also preferred by those who find the draft created by air coolers discomforting. Typical refrigerant used is “Freon”, a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants are commonly used due to their stability and safety properties.
A simple vapor compression cycle (VCC), FIG. 2, is some times referred to as Rankine cycle is composed of four operations:
1. Process 1-2: Isotropic compression, S=C. The refrigerant enters to the input of the compressor; it is pressured in a reverse adiabatic process with constant entropy and outputs at pressure Pc e.g. 28 bar.
The compressor's work done is the input work=Wc=m′(h2−h1)
Where m′ is the mass flow rate and h is the enthalpy.
2. Process 2-3: is the heat rejection to hot region@PC through the condenser.
The output refrigerant from the compressor is in liquid form.
The heat lost in the condenser is Qc=m′(h2−h3).
3. Process 3-4: Throttling process@h=c, is the throttling through the capillary or expander valve to a lower output pressure Pe (e.g. 11 bar or 1100 KPa) at the evaporator input. This is an adiabatic process without any work, i.e. h4=h3.
4. Process 4-1: Heat addition at cold region@P=C. Heat is gained by the refrigerant, which is a mixture of liquid and vapor and it exits in saturated vapor phase. This process happens at constant pressure.
The heat gained is given by the evaporator's load=Qe=m′(h1−h4).
Where one ton of refrigeration (T. R.) is given by 12,000 BTU/hr.
The refrigeration effect is the enthalpy difference between entering and exiting from the evaporator.RE=h2−h1 
The coefficient of performance (COP)=Qe/Wc RE/Wc=(h1−h4)/(h2−h1)
The mass flow rate is given by m′=Qe/RE
More recent approaches to air conditioning and climate control systems are disclosed in the following patents.
A U.S. patent of Dennis (U.S. Pat. No. 5,782,101) discloses a heat pump operating in the heating mode refrigerant pressure control. As disclosed therein, a heat pump system operates in the heat cycle mode wherein a sensor is provided for sensing either the pressure or temperature of a refrigerant. A speed controller receives an output of the sensor so that the speed of an evaporator fan is controlled, resulting in the control of the pressure or temperature of the refrigerant. The temperature or pressure of the refrigerant is controlled for a heat pump system comprising one refrigeration circuit and more than one refrigeration circuit.
A more recent patent of Wightman (U.S. Pat. No. 6,314,747) discloses a vapor compression system. As disclosed the system includes an evaporator, a compressor and a condenser interconnecting in a closed loop system. In one embodiment, a multifunctional valve is configured to receive a liquefied heat transfer fluid from the condenser and a hot vapor from the compressor. A saturated vapor line connects the outlet of the multifunctional valve to the inlet of the evaporator and is sized so as to substantially convert the heat transfer fluid exiting the multifunctional valve into a saturated vapor prior to delivery to the evaporator.
In a U.S. Pat. No. 6,378,323 of Chavagnat a reversible heat pump system includes heat exchangers having significantly different refrigerant handling capacities and a refrigerant holding device for holding excess refrigerant during the heating mode of operation. The refrigerant holding device includes a heat exchanger located therein for sub-cooling the refrigerant.
A more recent patent of Satzger (U.S. Pat. No. 7,080,520) discloses an air conditioning system based on a climate control system for a vehicle that is driven by an internal combustion engine. A heating heat exchanger is connected to a coolant loop of the engine and is preceded upstream of a blower by an evaporator and a compressor in a refrigerant loop. During a cooling mode, it pumps a refrigerant via a gas cooler and via an expansion valve to the evaporator and during a heating mode pumps into the evaporator bypassing the gas cooler and is disposed between the coolant loop and the refrigerant loop. A coupling heat exchanger is provided.
Finally, a U.S. patent of Ambs et al. (U.S. Pat. No. 7,228,696) discloses a hybrid heating and cooling system wherein the system includes an indoor air coil subcircuit, an outdoor air coil subcircuit, a geothermal subcircuit and a cooling system for selectively operating the system in air-to-air heating, air-to-air cooling, geothermal heating. The various subcircuits may be connected to one another in parallel.
Notwithstanding the above it is presently believed that there is a need for a high efficiency air conditioning and climate control system in accordance with the present invention. Such systems are believed to reduce the cost of operating such systems.